When San Francisco prosecutors dismissed charges against Kristian Aspelin in early December, it became just the latest case to raise questions about how shaken baby syndrome is diagnosed. Aspelin, who was accused of causing the death of his infant son, had one thing in his favor: He had enough money to pay for medical experts who cast doubt on the prosecution's theory.

Aspelin's nightmare began on a November afternoon two years ago. He had just brought his two sons home from day care. His 2-year-old son opened the refrigerator and dropped strawberries and pizza on the floor. Aspelin says he went to clean it up while holding his 3-month-old son, Johan.

"So I ran into the kitchen to address what was going on, and I brought Johan along with me in my right hand and eventually after cleaning up, slipped and fell," says Aspelin, who spoke publicly for the first time in an interview with NPR. "And I will never forgive myself for bringing Johan into the kitchen, but it was an accident."

Johan had fallen onto the tile floor.

Aspelin called 911 and an ambulance took the infant to the hospital. Five days after the fall, Johan died.

The San Francisco medical examiner did an autopsy and found injuries consistent with shaken baby syndrome. Aspelin was charged with felony assault of his son.

Earlier this month, prosecutors quietly dropped the charges after Aspelin's attorney presented reports from six medical experts and a biomechanical engineer. Those defense experts explained how the child's death was consistent with the fall Aspelin described and argued there was a lack of evidence to suggest the child was deliberately injured.

Aspelin's defense even hired a video company that made a model of the family's kitchen — the family had since moved — and filmed Aspelin, holding a doll, slipping on the floor.

"Before we did the reenactment," Aspelin says, "I didn't know if I would be able to, how I would react to go into that environment and try to relive those moments that have, you know, basically haunted me for, for a long time."

One issue was whether a child could die from a fall of just about three feet. The video showed how the child's head could have hit the hard tile.

Among the experts Aspelin hired were those who have testified on both sides of child abuse cases. Some explained how scientific knowledge about child deaths is changing, and how they have come to understand there are many alternative possibilities to what's often thought to be deliberate and violent shaking.

Patrick Barnes, a pediatric neuroradiologist and one of the experts hired by Aspelin's defense, explained how doctors now recognize "a variety of accidental and natural causes" that are sometimes overlooked in cases that are first diagnosed as shaken baby syndrome.

Barnes had testified for the prosecution in one of the most famous shaken baby syndrome cases — at the 1997 trial of English au pair Louise Woodward in Massachusetts. Since then he has come to believe that the syndrome is overdiagnosed and misdiagnosed.

Aspelin's attorney, Stuart Hanlon, agrees. "Innocent people get convicted, especially in these kind of cases," he says. "And we have to have a better way to protect people from false allegations of shaken baby."

To pay for his defense, Aspelin went through his savings, sold his house and borrowed from family and friends to raise more than $1 million. It cost about $100,000 just for the expert medical witnesses — a price that makes them unavailable to many defendants.

Last year, NPR News Investigations — with PBS' Frontline and ProPublica — found 23 cases of child deaths where charges were later reversed or dropped. Since then, a Texas man who was the focus of one story was released from prison. And in California, a woman who was the focus of another, had her sentence commuted.

A spokeswoman for San Francisco District Attorney George Gascon confirmed that the charges against Aspelin were dropped. Prosecutors — in an unusual arrangement — worked collaboratively with Aspelin's medical experts. In the end, the district attorney concluded there was not enough evidence, as the spokeswoman put it, "to prove the case beyond a reasonable doubt."

Still, Aspelin's troubles are far from over. Since the indictment, he's been required to live apart from his wife and their surviving son, who is now 4.

"He really kept us strong because we had something to really fight for," Aspelin says of his older son. "And I couldn't bear even thinking of losing our other son after Johan went away."

Aspelin can see his son every day — on supervised visits — but can't stay overnight in the house. It will take another legal proceeding to be reunited.

Copyright 2013 NPR. To see more, visit http://www.npr.org/.

Transcript

ROBERT SIEGEL, HOST:

From NPR News, this is ALL THINGS CONSIDERED. I'm Robert Siegel.

MELISSA BLOCK, HOST:

And I'm Melissa Block. Prosecutors in San Francisco have dismissed the charges against a man accused of killing his infant son. It's just the latest case to raise questions about the diagnosis of shaken baby syndrome, and whether it's sometimes misapplied. As NPR's Joseph Shapiro reports, the father had one key advantage: He had enough money to pay for medical experts who cast doubt on the prosecution's theory.

JOSEPH SHAPIRO, BYLINE: Here's how Kristian Aspelin's nightmare began. On a November afternoon two years ago, he called 911.

(SOUNDBITE OF ARCHIVED 911 CALL)

UNIDENTIFIED WOMAN: Do you need a paramedic right now, sir?

KRISTIAN ASPELIN: Uh, I don't know. I dropped my baby and he's - went - he's still breathing and so forth...

UNIDENTIFIED WOMAN: Right. Now, let me send you a paramedic. What is the address?

SHAPIRO: Aspelin's older, 2-year-old son had opened the refrigerator, and dropped strawberries and pizza on the floor. Aspelin says he walked in to clean it up, holding onto his 3-month-old son, Johan. But then he slipped, fell backwards, and dropped the baby on the tile floor. Now, the father is speaking publicly for the first time, in this interview with NPR.

ASPELIN: So I ran into the kitchen to address what was going on; and I brought Johan along with me, in my right hand and eventually, after cleaning up, slipped and fell. And you know, I will never forgive myself for bringing Johan into the kitchen, you know. But it was an accident.

SHAPIRO: Five days after the fall, the child died in a hospital. The San Francisco medical examiner did an autopsy, and found injuries consistent with shaken baby syndrome. Aspelin was charged with causing the death of his son. But earlier this month, prosecutors in San Francisco quietly dropped the charges, after Aspelin's attorney presented reports from six medical experts and one biomechanical engineer. Those defense experts explained how the child's death was consistent with the fall described by the father; and argued there was a lack of evidence to suggest the child was deliberately injured.

ASPELIN: We re-created our old kitchen in a warehouse.

SHAPIRO: Aspelin's defense even hired a video company that made a model of the family's kitchen and filmed Aspelin, holding a doll, slipping on the floor.

ASPELIN: Before we did the re-enactment, I didn't know if I would be able to - how I would react to going into that environment, and try to relive those moments that have, you know, basically haunted me for a long time.

SHAPIRO: One issue was whether a child could die from a short fall of just about 3 feet. The video showed how the child's head could have hit the hard tile. Now, if you're thinking that Aspelin and his lawyer just went out and found seven expert guns-for-hire, that's not what happened. There were experts who've testified on both sides in child abuse cases. Some explained how scientific knowledge about child deaths is changing, and how they've come to understand there are many alternative possibilities to what's often thought to be deliberate and violent shaking. Stuart Hanlon is Aspelin's attorney.

STUART HANLON: Innocent people get convicted, especially in these kind of cases. And we have to have a better way to protect people from false allegations of shaken baby.

SHAPIRO: For his defense, Aspelin went through his savings, sold his house, borrowed from family and friends; to raise over a million dollars. It cost about a hundred thousand dollars just for the expert medical witnesses - a price that makes them unavailable to many defendants. Last year, NPR's investigative unit, with PBS Frontline and ProPublica, found 23 cases of child deaths where charges were later reversed or dropped. Since then, a Texas man who was the focus of one of our stories, was released from prison. And in California, a woman who was the focus of another, had her sentence commuted.

No one from the San Francisco D.A.'s office would speak on tape. But a spokeswoman confirmed that prosecutors, in an unusual arrangement, worked collaboratively with Aspelin's medical experts. In the end, the district attorney concluded there was not enough evidence - as the spokeswoman put it - to prove the case beyond a reasonable doubt.